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ENERGY USED IN ELECTRIC
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See also:ENERGY USED IN ELECTRIC See also:WELDING has another valuable effect in properly distributing the See also:heating over the whole See also:section of the See also:joint. Any portion which may be for the moment at a See also:lower temperature than other portions will necessarily have a lower relative resistance, and more current will be diverted to it. This See also:action rapidly brings any cooler portion into equality of temperature with the See also:rest. It also prevents the over-heating of the interior portions which are not losing See also:heat by See also:radiation and convection. The success of the electric See also:process rn welding metals which were not formerly regarded as weldable is probably due in a measure to this cause, and also to the ease of See also:control of the operation, for the operator may See also:work within far narrower limits of plasticity and fusibility than with the forge See also:fire or See also:blowpipe. The See also:mechanical pressure may be automatically applied and the current automatically cut off after the completion of the weld. In some more See also:recent types of welders the clamping and releasing of the pieces are also accomplished automatically, and nothing is See also:left for the operator to do but to feed the pieces into the clamps. Repetition-work is thus rapidly and accurately done. The automatic welder represented in fig. 3 has a capacity of nearly moo welds per See also:day. The pressure required is subject to considerable variation: the more rigid the material at the welding temperature, the greater is the necessary pressure. With See also:copper the force may be about boo pounds per square See also:inch of section; with wrought See also:iron, 1200 pounds; and with See also:steel, i800 pounds. It is customary to begin the operation with a much lighter pressure than that used when all parts of the pieces at the joint have come into contact. The pressure exerted in completing the weld has the effect of extruding from the joint all dross and slag, together with most of the See also:metal which is rendered plastic by the heat. The strongest electric welds are those effected by this extrusion from the joint, in consequence of heavy pressure quickly applied at the See also:time of completion of the weld. The unhammered weld, as ordinarily made by the electric process, has substantially the same strength as the annealed metal of the See also:bar, the break under tensile See also:strain, when the See also:burr at the weld is left on, usually occurring a little to one See also:side of the joint proper, where the metal has been annealed by heating. Hammering or See also:forging the joint while the metal cools, in the See also:case of malleable metals such as iron or copper, will usually greatly toughen the metal, and it should be resorted to where a maximum of strength is desired. The same See also:object is partially effected by placing the weld, while still hot, between See also:dies pressed forcibly together so as to give to the weld some desired See also:form, as in drop-forging. The amount of electric energy necessary for welding by the See also:Thomson process varies with the different metals, their electric conductivity, their heat conductivity, fusibility, the shape of the pieces, section at the joint, &c. In the following table are given some results obtained in the working of iron, See also:brass and copper. The figures are of course only approximate, and refer to one See also:condition alone of time-See also:consumption in the making of each weld. The more rapidly the work is done, the less, as a See also:rule, is the See also:total energy required; but the See also:rate of output of the plant must be increased with increase of See also:speed, and this involves a larger plant, the consequent expense of which is often disadvantageous. If in the following Iron and Steel. Section, Sq. In. See also:Watts in See also:Prim- Time in See also:Watt-seconds. ary of welder. Secs. 0.5 8,500 33 280,500 I.0 16,700 45 751,500 1.5 . 23,500 55 1,292,500 2.0 29,000 65 I,885,00o 2.5 34,000 70 2,380,000 3.0 39,000 78 3,042,000 3.5 • 44,000 85 3,740,000 4.0 . 50,000 90 4,500,000 Brass. •25 . 7,500 17 127,500 5 13,500 22 297,000 '75 . 19,000 29 551,000 1.0 25,000 33 825,000 1.25 . 31,000 38 1,178,000 1.5 . 36,000 42 1,512,000 1.75 . 40,000 45 I ,800,000 2.0 44,000 48 2,112,000 Copper. •125. 6,00o 8 48,000 .25 . 14,000 11 154,000 '375. 19,000 13 247,000 .5 . 25,000 16 400,000 .625. 31,000 18 558,000 •75 . 36,500 21 766,500 '875. 43,000 22 946,000 L 1•o 49,000 23 1,127,000 In practice, See also:joints in solid bars or in wires are the most See also:common, but the process is applicable to pieces of quite varied form. Joints in iron, brass, or See also:lead See also:pipe are readily made; strips of See also:sheet metal are joined, as in See also:band saws; bars or tubes are joined at various angles; sheet metal is joined to bars, &c. One of the more interesting of the recent applications of electric welding is the See also:longitudinal seaming of thin steel pipe. The metal or skelp is in See also:long strips, See also:bent to form a hollow See also:cylinder or pipe, and the longitudinal seam moves through a See also:special welder, which passes a current across it. The work is completed by See also:drawing the pipe through dies. The welding of a See also:ring forrned by bending a See also:short bar into a circle affords an excellent See also:illustration of the See also:character of the currents employed in the Thomson process. Notwithstanding the comparatively See also:free path around the ring through the See also:lull section of the bent bar, the current heats the abutted ends to the welding temperature. In this way waggon and See also:carriage See also:wheel tyres, See also:harness rings, See also:pail and See also:barrel hoops, and similar See also:objects are extensively produced. The process is also largely applied to the welding of iron and copper wires used for electric lines and conductors, of steel axles, tyres and metal frames used in carriage work, and of such parts of bicycles as pedals, See also:crank hangers, seat posts, forks, and steel tubing for the frames. The heat, whether it be utilized in welding or brazing, is so sharply localized that no damage is clone to the finish of surfaces a short distance from the weld or joint. Parts can be accurately formed and finished before being joined, as in the welding of See also:taper shanks to drills, the lengthening of drills, See also:screw taps, or augers, and the like. Electric welding is applicable to forms of pieces or to conditions of work which would be impracticable with the See also:ordinary forge fire or See also:gas blowpipe. A characteristic instance is the See also:wire bands which hold in See also:place the solid See also:rubber tyres of vehicles. The proximity of the rubber forbids the application of the heat of a fire or blowpipe, but by springing the rubber back from the proposed joint and seizing the ends of wire by the electric welding clamps, the See also:union is rapidly and easily made. When the rubber of the See also:tyre is released, it covers the joint, regaining its See also:complete form. Special manufactures have in some cases arisen based upon the use of electric welding. The welding clamps, and the mechanical devices connected with them, vary widely in accordance with the work they have to do. A See also:machine for forming metal wheels is so constructed that the hubs are made in two sections, which when brought together in the welder are caused to embrace the radiating iron or steel spokes of the wheel. The two sections are then welded, and hold the spokes in solid union with themselves. Another machine, designed for the manufacture of wire fences,makes several welds automatically and simultaneously Galvanized iron wires are fed into the machine from reels in several parallel lines about a See also:foot apart, and at intervals are crossed at right angles by wire sections cut automatically from another See also:reel of wire. As the wire passes, electric welds are formed between the transverse and the parallel lines. The machine delivers a continuous See also:web of wire See also:fencing, which is See also:wound upon a See also:drum and removed from time to time in large rolls. In the See also:United States, See also:street railway rails are welded into a continuous metal structure. A huge welding transformer is suspended upon a See also:crane, which is See also:borne upon a See also:car arranged to run upon the track as it is laid. The joint between the ends of two contiguous rails is made by welding lateral strap pieces, covering the joint at each side and taking the place of the ordinary See also:fish-plates and bolts. The exertion of a greatly increased pressure at the finish of the welding seems to be decidedly favourable to the permanence and strength of the joints. When properly made, the joint is strong enough to resist the strains of See also:extension and See also:compression during temperature changes. For electric See also:railways the welded joint obviates all See also:necessity for " bonding " the rails together with copper wires to convert them into continuous lines of return conductors for the railway current. In railway welding the source of energy is usually a current delivered from the trolley See also:line itself to a rotary converter mounted on the welding car, whereby an alternating current is obtained for feeding the See also:primary See also:circuit of the welding transformer. See also:Power from a distant station is thus made to produce the heat required for track welding, and at exactly the place where it is to be utilized. In this instance the work is stationary while the welding apparatus is moved from one joint to the next. Welding See also:transformers are sometimes used to heat metal for See also:annealing, for forging, bending, or shaping, for tempering, or for hard soldering. Under special conditions they are well adapted to these purposes, on See also:account of the perfect control of the heating or energy delivery, and the rapidity and cleanliness of the operation. Divested of its welding clamps, the welding transformer has found a unique application in the See also:armour-annealing process cf Armoue+ Lemp, by means of which spots or lines are locally annealed See also:plate in hard-faced See also:ship's armour, so that it can be drilled or plate cut as desired. Before the introduction of this process, it was practically impossible to render any portion of the hardened See also:face of such armour workable by cutting tools without detriment to the hardness of the rest. A very heavy electric current is passed through the spot or See also:area which it is desired to soften, so that, notwithstanding the rapid See also:conduction of heat into the See also:body of the plate, the metal is brought to a See also:low red heat. In See also:order that the spot shall not reharden, it is requisite that the rate of cooling shall be slower than when the heating current is cut off suddenly, the current therefore undergoes See also:gradual diminution, under control of the operator. The welding transformer has for its secondary terminals simply two copper blocks fixed in position, and mounted at a distance of an inch or more apart. These are placed firmly against the face of the armour plate, with the spot to be annealed bridging the contacts, or situated between them. As in track welding, the transformer is made movable, so that it can be brought into any position desired. When the annealing is to be done along a line, the secondary terminals, with the transformer, are slowly and steadily slid over the face of the plate, new portions of the plate being thus continually brought between the terminals, while those which had reached the proper heat are slowly removed from the terminals and cool gradually. (E. 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